1. Field of the Invention
The invention relates to a humidity sensor which has, on a substrate, at least one voltage sensor with a sensor region and at least one control electrode that is connected to a signal source designed such that a variable control voltage can be applied to the control electrode, wherein a moisture-permeable sensor layer whose dielectric constant depends on humidity is located on the sensor region adjacent to the control electrode, wherein the control electrode is adjacent to the sensor layer in such a manner that the measured voltage signal of the voltage sensor depends on the control voltage and the humidity, and wherein the voltage sensor is connected to an analysis unit for ascertaining the humidity on the basis of the measured voltage signal.
2. Description of the Background Art
A humidity sensor of this nature is known from EP 1 176 418 A2. The humidity sensor has a semiconductor chip in which a field-effect transistor is integrated as the voltage sensor. In a semiconductor substrate, the field-effect transistor has a drain and a source between which a channel region is formed as a voltage-sensitive sensor region. Located on the channel region is a gas-sensitive sensor layer that is polarizable independently of the humidity and whose dielectric constant depends on the humidity. The sensor layer is made of a porous, gas-permeable material. Located on the sensor is a control electrode, which likewise is porous and gas-permeable and completely covers both the sensor layer and a passivation layer that is laterally contiguous therewith. To measure the humidity, a voltage is first applied to the control electrode in order to determine the humidity-dependent change in the relative dielectric constant. The humidity is then ascertained using the measured change. The humidity sensor has the disadvantage that an additional fabrication step is required during its fabrication, after the application of the sensor layer on the channel region, in which a porous metallization is applied as the control electrode to the sensor layer and the passivation layer laterally contiguous therewith. The metallization must adhere to the sensor layer and the passivation layer. This results in certain restrictions in the choice of materials for the metallization and the sensor layer. It is also unfavorable that only porous, gas-permeable layers can be used as metallization.